WASHINGTON — The chairman of the Senate finance panel requested Lawyer Basic Merrick B. Garland on Tuesday for details about whether or not Credit score Suisse continued to assist wealthy Individuals defraud the I.R.S. even after it signed a settlement settlement with the Justice Division vowing to cease the apply.

At challenge is a retired professor named Dan Horsky, whom Credit score Suisse helped to evade tax funds on $200 million in belongings. A whistle-blower made federal prosecutors conscious of Mr. Horsky’s account in the summertime of 2014, and it clearly violated the phrases of the settlement settlement that Credit score Suisse had agreed to only weeks earlier.

However the Justice Division underneath the Obama and Trump administrations by no means punished Credit score Suisse for violating the deal, although the whistle-blower’s data led Mr. Horsky to plead guilty to tax evasion in 2016.

Senator Ron Wyden, Democrat of Oregon and chairman of the Senate Finance Committee, requested Mr. Garland for extra details about the Horsky account and the rest that may present whether or not Credit score Suisse executives made false statements to Congress, to the Justice Division and to the courts when it mentioned it vowed to cooperate with U.S. authorities efforts to pressure the wealthiest Individuals to pay their taxes.

The scrutiny round Credit score Suisse’s non-public wealth administration practices comes at a delicate time for the financial institution. Final week it reported important losses due to loans it made to a collapsed funding agency and mentioned that Switzerland’s monetary regulator would examine the financial institution’s danger administration practices. Regulators are additionally investigating a spying scandal and the sale of billions of dollars worth of investments that had been harking back to the shoddy subprime mortgage bonds that led to the 2008 world monetary disaster.

“Public experiences and federal court docket paperwork elevate necessary questions as as to if Credit score Suisse has totally complied with its plea settlement,” Mr. Wyden wrote in a letter to Mr. Garland.

“The plea settlement is expressly contingent on Credit score Suisse’s efficiency of all of its materials obligations,” Mr. Wyden added; it “specifies that if Credit score Suisse ought to fail to totally carry out its obligations, the ‘settlement to not additional prosecute shall be null and void.’”

Ought to prosecutors determine that Credit score Suisse violated its settlement with the Justice Division, the financial institution might be uncovered to authorized legal responsibility and extra fines.

Mr. Wyden requested the Justice Division for a briefing on the Horsky case by Might 11.

A spokesman mentioned that the Justice Division had obtained the letter, however had no speedy remark. A Credit score Suisse spokeswoman mentioned that because the 2014 settlement, the corporate “has cooperated totally with U.S. authorities and can proceed to take action.”

Mr. Wyden additionally requested that the division assist him confirm whether or not Credit score Suisse executives offered false statements to the Senate in February 2014, after they testified about whether or not the financial institution had stopped serving to rich Individuals evade taxes.

Brady Dougan, then Credit score Suisse’s chief govt, informed senators that the financial institution had labored to be “one hundred pc compliant with the necessities across the U.S. taxpayer,” Mr. Wyden wrote. On the similar listening to, the financial institution’s basic counsel, Romeo Cerutti, testified that Credit score Suisse was “actually taking a look at whether or not somebody is a U.S. individual” with a purpose to root out Individuals who had been hiding their wealth from the I.R.S.

For almost 15 years, Republicans and Democrats have taken half in a well-publicized marketing campaign to weed out tax dodgers with Swiss financial institution accounts, specializing in UBS and Credit score Suisse, each headquartered in Zurich.

When the Credit score Suisse executives testified in 2014, they had been within the midst of negotiations with the Justice Division a couple of settlement over the financial institution’s therapy of U.S. tax dodgers.

The 2 sides signed the deal in Might 2014, by which Credit score Suisse pleaded guilty to serving to some American purchasers evade taxes and was fined a complete of $2.6 billion. Nevertheless it averted even larger fines as a result of it vowed to federal prosecutors that it had stopped the apply, would shut “any and all accounts of recalcitrant account holders,” and would assist the U.S. pursue different felony investigations.

The responsible plea and steep fantastic had been uncommon in 2014, and it was the primary time in additional than 20 years {that a} lender of its measurement had admitted wrongdoing in an American court docket.

However a whistle-blower emerged in July of that 12 months and informed officers on the tax division of the Justice Division and federal prosecutors who had labored on the case about an account that belonged to Mr. Horsky, a retired enterprise professor who lived in Rochester, N.Y. and amassed a lot of his fortune by investing in start-up corporations within the Nineties, in keeping with information accounts.

In September 2014, when Credit score Suisse appeared in court docket to plead responsible, the choose requested each the financial institution and prosecutors whether or not they had any data that may have an effect on the settlement settlement. Either side mentioned no.

However the whistle-blower tip led prosecutors to find that Mr. Horsky had hidden a $200 million fortune with the assistance of Credit score Suisse bankers utilizing offshore shell corporations, court docket paperwork present. The association lasted for months after the financial institution signed its plea deal.

As a part of the scheme to cover Mr. Horsky’s wealth, bankers put it underneath the identify of one among Mr. Horsky’s family members who lived abroad. When an account of that measurement adjustments palms, it’s topic to enhanced due diligence, which incorporates notifying financial institution executives of the change.

Mr. Wyden additionally despatched a letter to Credit score Suisse on Tuesday searching for details about when the Justice Division informed Credit score Suisse in regards to the Horsky account. He requested whether or not the financial institution notified the federal government of the account earlier than the whistle-blower got here ahead, and if not, whether or not that was the results of poor inner controls or “a willful determination to not report the existence of those accounts to U.S. authorities entities.”

It’s unclear why the Justice Division didn’t notify the court docket of the whistle-blower declare and alter the phrases of its settlement. The division would have had the authority to overview the Credit score Suisse case for potential breaches and additional prosecute the financial institution.

Jack Ewing contributed reporting.